Pipelines are used to transport fluid materials such as liquids or gasses across long distances, over and under land and water. In the U.S. alone, several million miles of pipelines are used to carry water, oil, natural gas, and other resources from one point to another. Pipelines are typically built as large hollow cylindrical conduits constructed by successively joining individual pipe segments to form a tubular pipeline of virtually any desired length. The material, diameter, and other physical characteristics of a pipeline vary depending on the material to be transported, the required volumetric flow rate to transport, and the structural and environmental conditions to which the pipeline is expected to be subjected. For example, steel pipelines having a diameter of over sixty inches are often used to transport large volumetric flow rates of water and other liquids. Steel pipelines having diameters ranging from under six inches to over twelve feet are common, with larger and smaller diameters sometimes used for specific applications.
Because pipelines are routed underground or above ground as necessary, and span vast lengths, they are often subjected to ground induced actions that apply forces to the pipelines that may threaten their structural integrity. For example, seismic events, in the form of seismic wave actions; or permanent ground deformations, such as a fault movement, liquefaction-induced settlement/uplifting and lateral spreading, or landslide motion, all induce movement and inflict forces upon portions of the pipeline. Data collected from pipelines subjected to earthquakes show that permanent ground deformations are the primary source of threat for buried pipeline integrity, usually resulting in bending and deformation of portions of the pipeline.
Various standards and criteria applicable to the construction of pipelines are known and used within the pipeline industry to define allowable limits and quantify pipeline performance. For example, with respect to water-carrying pipelines, the primary performance criteria is “no loss of containment” upon occurrence of a seismic or other movement event. In view of those criteria, pipe segments are not normally linked by gasket joint systems where significant seismic action is expected, instead the pipe joints are welded to provide a more secure attachment between segments.
Welded pipeline joints may take various forms, including butt-welded, where two plane ends of adjoining pipe segments are aligned and welded, and lap-welded, where an expanded end (bell) of one pipe segment is placed over a stub end (spigot) of an adjoining pipe segment and welded. Lap welded joints are either single welded (a weld on one end of the spigot or bell) or double welded (a weld on both the bell and spigot-end of the lap joint).
Welded-lap joints have been extensively used in steel water pipelines rather than butt-welded joints because of they typically have lower installation costs. However, even though more favored for field assembly than butt-welded joints, industry data shows that welded-lap joints may constitute a weak point in the pipeline. Because of their geometry and the resulting stress path the bell eccentricity creates, under severe compressive loading conditions welded-lap joints are prone to fail—typically in the form of wrinkles occurring as localized deformation and folding at the bell eccentricity. This deformation may lead to fracture of the pipeline due to excessive local tensile strain or fatigue under operational loading conditions.
Thus, there remains a need in the art for an improved apparatus and method for joining pipe segments in a pipeline to provide superior strength, resilience, and resistance to failure under movement conditions.